This invention relates generally to the use of body fluid-soluble nuclear matrix proteins as cellular markers. More particularly, the invention relates to a method of monitoring the degree of cell death in a tissue by monitoring the level of interior nuclear matrix proteins and/or fragments thereof released from cells in a body fluid-soluble form.
Cell death occurs as a function of healthy tissue homeostasis, as well as a result of disease or injury to the tissue. Detectable changes in the rate of cell death in a tissue therefore can provide an indication of the tissue""s status. In normal growing tissue, for example, changes in the rate of cell death can indicate a new developmental stage. Alternatively, a sudden detected change in cell death in adult tissue can signal an injury to the tissue and also provide information on the type of injury. Previously, clinical assessment of tissue viability has required presentation of clinical symptoms and a visual inspection of the tissue itself, requiring observation of the morphology of cells in a tissue sample, and/or an indirect estimation of cell death by measuring changes in tissue/organ size. While the state of the art of morphological observation has advanced significantly, reliance on histological observation of an abnormality requires that the abnormal cells comprise part of the tissue sample tested. Early stages of a malignancy therefore can be particularly difficult to detect by this method. Biochemical assessments of cell or tissue viability also generally have been difficult to interpret, primarily because in many instances cell death occurs in individual cells which are intimately intermixed with viable cells in a sample.
There exists a need for reliable means of monitoring the degree of cell death in a tissue which does not rely on histology or tissue biopsy. A particularly useful method would be one wherein the rate of cell death could be monitored in a body fluid assay. It is anticipated that the ability to accurately monitor tissue-specific cell death in a fluid assay would have significant impact on the study of tissue development and cell kinetics, as well as on many different clinical applications. For example, the method may be used to monitor the progress of a disease or injury associated with cell death, as well as to monitor the efficacy of a therapy for an affected tissue. The method also may be used to monitor the effect of the therapy on unaffected, normal tissue. In addition, the method may be used to evaluate a compound""s cytotoxicity.
Recently, methods have been disclosed for extracting and isolating the normally highly insoluble interior nuclear matrix proteins from cells. Interior nuclear matrix proteins are proteins from within the boundaries of the nuclear matrix, termed xe2x80x9cinteriorxe2x80x9d nuclear matrix proteins, which are substantially free of chromatin proteins, and intermediate filaments, collectively termed xe2x80x9cexteriorxe2x80x9d nuclear matrix proteins (see Penman et al., U.S. Pat. No. 4,882,268, the disclosure of which is hereby incorporated by reference). In the method, the cell nucleus is isolated, the cytoskeleton proteins and chromatin are removed, the xe2x80x9cnuclear matrixxe2x80x9d is isolated, and the interior and exterior components of the nuclear matrix are separated. The nuclear matrix-intermediate filament complex comprises a specific fraction of cell protein constituting less than five percent of the total protein and six percent of the total DNA of the cell. The interior nuclear matrix comprises about one percent or less of the total cellular protein. It contains many proteins that differ according to cell type, and is highly enriched with type-specific antigens including cell-type and transformation-specific proteins that had not been detected using prior art procedures. It also contains the lamina and nuclear pore complex proteins. The separation method makes use of the unique properties of the nuclear matrix to achieve separation from substantially all other cell constituents. The method is simple, rapid, reproducible, achieves a high degree of purity, and is applicable to essentially all types of cells.
The method of Penman et al. has enabled the art to identify and isolate cell type-specific and transformation-specific interior nuclear matrix proteins of sufficient purity to allow antibodies to be made. These antibodies then can be used to detect cell type-specific interior nuclear matrix proteins in a sample, as disclosed in U.S. Pat. No. 5,273,877, the disclosure of which is incorporated herein by reference. As used therein and. here, the term xe2x80x9ccell-typexe2x80x9d is understood to refer to cells of various different tissues such as neural, glial, muscle, liver, mesenchymal, and different types of epithelia and endothelia, as well as malignant cell forms and cells having an altered genomic expression profile caused by viral infection or other factors.
It is an object of this invention to provide a method for monitoring the degree of cell death in a body fluid assay by monitoring the level of body fluid-soluble interior nuclear matrix proteins in a fluid. Another object of the invention is to provide a method for quantifying the body fluid-soluble interior nuclear matrix proteins released from cells and present in a cell compatible fluid. Still another object of the invention is to provide a method for evaluating a therapy, or the progress of a disease associated with cell death by monitoring the degree of cell death in an affected tissue. Another object of the invention is to provide a method for assessing the toxicity of compounds by assessing their ability to induce cell death. Still another object of the invention is to provide a method for inducing the release of body fluid-soluble nuclear matrix proteins from eucaryotic cells. These and other objects and features of the invention will be apparent-from the description and claims which follow.
It now has been discovered that interior nuclear matrix proteins or soluble fragments thereof are released in soluble form from cells undergoing cell death. As used herein, xe2x80x9ccell deathxe2x80x9d is understood to include both apoptosis (xe2x80x9cprogrammedxe2x80x9d cell death), and necrosis. moreover, it also now has been discovered that these soluble forms of interior nuclear matrix proteins can be quantitated in a fluid and used to monitor the degree, or rate, of cell death in a tissue. The method of the invention also may be used to distinguish between types of cell death occurring. The presence of these proteins and protein fragments in solution in a body fluid soluble form is unexpected as the molecules comprise part of an insoluble nuclear complex under standard physiological conditions. The discovery of these proteins released in soluble form from dying cells allows one to use the soluble interior nuclear matrix proteins as biochemical monitors of tissue-specific cell death in fluid assays. The method is rapid and quantitative and can be used to evaluate the viability of cells and tissue, to evaluate progress of a disease and/or its treatment, to evaluate the cytotoxicity of unknown compounds and to study the kinetics of cell death. The discovery also provides an alternative method for purifying interior nuclear matrix proteins from cells.
The method of the invention involves detecting the concentration of body fluid-soluble interior nuclear matrix proteins or fragments thereof released from cells and comparing this concentration to a known standard. The concentration of these proteins in a body fluid sample will be indicative of the degree of cell death in that tissue. Fluid samples are collected at discrete intervals and detected by means, for example, of an immunoassay. The concentrations of characteristic proteins then are compared, with changes in concentrations being indicative of the changes in the rate of cell death. In addition, certain proteins may be identified as cell type-specific and/or as cell death type-specific. Exemplary body fluids include blood, serum, plasma, urine, semen, spinal fluid, saliva, ascitic fluid, peritoneal fluid, sputum, tissue swabs, and body exudates such as breast exudate.
In one embodiment of the invention, the method may be used to evaluate the progress of a disease. For example, the method may be used to monitor the progress of a malignancy such as, for example, a carcinoma, adenoma, sarcoma, lymphoma, or myeloma. Here the rate of cell death in a malignant tissue may be monitored by quantitating the level of soluble nuclear matrix protein released from the malignant cells. Alternatively, the method also may be used to monitor the progress of tissue disorders resulting in altered cell death, such as results from tissue atrophy, hyperplasia, cirrhosis, hypoxia, ischaemia and benign tumor growths. Injured tissue also can be assessed by this method, including direct cell trauma such as from membrane-active chemicals and toxins or resulting from direct physical trauma, such as, for example, hyperthermia, hypoxia and ischemia/reperfusion, radiation or complement-mediated autolysis.
In another embodiment of the invention, the method may be used to monitor the efficacy of a therapy. Here a therapeutic agent or procedure (e.g., radiation therapy) is administered to a patient and, thereafter, the concentration of soluble nuclear matrix proteins or fragments are detected in body fluid samples drawn from the patient at predetermined intervals. These concentrations then are compared to each other and to those in samples tested before administration of the therapy. The changes in concentration of one or more interior nuclear matrix proteins detected among the samples compared will be indicative of the therapy""s efficacy. For example, a therapeutic agent capable of selectively destroying malignant cells can cause an increase in soluble nuclear matrix proteins released from the tumor cells, followed by a reduction in the level of these proteins detected as the number of malignant cells fall. The method also may be used to monitor the effect of a given therapy on the viability of normal, unaffected tissue. For example, a number of cancer therapies, including radiation and chemotherapy, target rapidly proliferating cell populations and therefore can affect normally proliferative cell populations such as bone marrow progenitor cell populations and intestinal epithelial cells. The effect of the therapy on these cell populations can be evaluated by monitoring the level of soluble interior nuclear matrix protein released from these cells. It is anticipated that a single body fluid sample can provide information on the viability of both the affected tissue and normal tissue provided that cell-type specific proteins can be monitored for each tissue. Similarly, the method also may be used to evaluate the efficacy of complementary therapeutic agents designed to protect normal tissue from the effects of the therapy.
In yet another embodiment of the invention the method may be used to evaluate the type of cell death occurring and to study its kinetics. For example, nuclear matrix proteins or protein fragments may be identified that are preferentially released in soluble form by cells undergoing either apoptosis or necrosis. The rate of release of these proteins or protein fragments then may be monitored to investigate cell death kinetics.
In still another embodiment of the invention the method may be used to monitor the status of a cell culture and/or to assess the cytotoxicity of a compound by monitoring the levels of soluble interior nuclear matrix proteins or protein fragments released from these cells. Finally, the method also may be used to induce release of body fluid-soluble interior nuclear matrix proteins from intact cells, using compounds capable of inducing apoptosis, such as, for example, cytokines. A particularly useful cytokine is TNF (Tumor Necrosis Factor). This embodiment of the invention may be used to enhance identification of particular interior nuclear matrix proteins. It further may be used as part of a protocol to isolate soluble interior nuclear matrix proteins or protein fragments. Novel nuclear matrix proteins may be obtained by this method, as well as known or novel proteins useful as antigenic determinants in antibody production. Finally, the method of the invention may be useful as part of a protocol to identify candidate compounds useful as cancer chemotheapeutic agents (see infra.)
These and other embodiments and features of the invention will be apparent from the specification, drawings and claims, which follow.